A shadow brightening method includes receiving, at a memory device, an original input image, a brightening level, and a threshold pixel intensity. If a pixel intensity is greater than the threshold, then the pixel is considered bright. Otherwise, the pixel is shadowed. The method includes calculating a gamma transformation for each pixel. If the pixel intensity is less than or equal to the threshold, then a gamma transformation equal to the received brightening level is applied. If the pixel intensity is greater than the threshold, then the gamma transformation is scaled to decrease with intensity. For each shadowed pixel, the method includes computing a minimum value. It also includes determining the brightening level to be applied, thus creating a gamma map. The method also includes applying the determined brightening level to the shadowed pixels and outputting a shadow-brightened output image.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A shadow brightening method, comprising: receiving, at a memory device, an input image having a plurality of pixels including that each pixel of the pixels specifies an input intensity, wherein a respective gamma is associated with each of the pixels; determining, via a processor, from the input intensity of each pixel of the pixels that the pixel is one of dark, transitional, and bright, wherein the pixel is dark when the input intensity of the pixel is less than or equal to a specified threshold, otherwise the pixel is transitional when the input intensity of the pixel is less than a crossover threshold, and otherwise the pixel is bright; for each pixel of the pixels that is dark, setting, via the processor, the respective gamma of the pixel to a specified brightening level; for each pixel of the pixels that is transitional, setting, via the processor, the respective gamma of the pixel to a scaling function of the input intensity of the pixel, wherein, over a range of the input intensity from the specified threshold to the crossover threshold, the scaling function monotonically increases from the specified brightening level at the specified threshold until the scaling function equals one at the crossover threshold; for each pixel of the pixels that is bright, setting, via the processor, the respective gamma of the pixel to a value of one, so that the pixel remains unchanged; calculating, via the processor, an output intensity of each pixel of the pixels from a gamma transformation of the input intensity of the pixel and the respective gamma of the pixel; and outputting, via the processor, a shadow-brightened output image having the pixels including that each pixel of the pixels specifies the output intensity of the pixel.
2. The method of claim 1 , wherein the method further comprises inputting the specified brightening level that is less than one and the specified threshold that is greater than zero and less than one from an end user.
3. The method of claim 1 , wherein the input image is one of a still image and an image from a video.
4. The method of claim 1 , wherein the specified brightening level and the specified threshold are based on histogram metrics.
5. The method of claim 1 , before the calculating step, grouping those of the pixels that are dark into smaller groups of a predetermined number and, for each pixel that is in the smaller groups, setting the respective gamma of the pixel to a value of one, so that the pixel remains unchanged.
6. The method of claim 1 , wherein the input image is color image, and the method further comprises the step of: converting the color image to an intensity image specifying the input intensity for each of the pixels.
7. A shadow brightening system, comprising: a memory device configured to receive an input image having a plurality of pixels including that each pixel of the pixels specifies an input intensity, wherein a respective gamma is associated with each of the pixels; and a processor configured to: determine from the input intensity of each pixel of the pixels that the pixel is one of dark, transitional, and bright, wherein the pixel is dark when the input intensity of the pixel is less than or equal to a specified threshold, otherwise the pixel is transitional when the input intensity of the pixel is less than a crossover threshold, and otherwise the pixel is bright; for each pixel of the pixels that is dark, set the respective gamma of the pixel to a specified brightening level; for each pixel of the pixels that is transitional, set the respective gamma of the pixel to a scaling function of the input intensity of the pixel, wherein, over a range of the input intensity from the specified threshold to the crossover threshold, the scaling function monotonically increases from the specified brightening level at the specified threshold until the scaling function equals one at the crossover threshold; for each pixel of the pixels that is bright, set the respective gamma of the pixel to a value of one, so that the pixel remains unchanged; calculate an output intensity of each pixel of the pixels from a gamma transformation of the input intensity of the pixel and the respective gamma of the pixel; and output a shadow-brightened output image having the pixels including that each pixel of the pixels specifies the output intensity of the pixel.
8. The system of claim 7 , wherein the input image is one of a still image and an image from a video.
9. The system of claim 7 , wherein the specified brightening level and the specified threshold are based on histogram metrics.
10. The system of claim 7 , wherein the input image is color image, and the processor is further configured to: convert the color image to an intensity image specifying the input intensity for each of the pixels.
11. The method of claim 1 , wherein, the output intensity from the gamma transformation monotonically decreases over the range of the input intensity from the specified threshold to the crossover threshold, in which range the scaling function, which provides the respective gamma for each pixel that is transitional, monotonically increases.
12. The method of claim 1 , further comprising: capturing the input image via a camera.
13. The method of claim 1 , wherein the calculating of the output intensity from the gamma transformation includes, for each pixel of the pixels, setting the output intensity of the pixel to the input intensity of the pixel raised to a power that is the respective gamma of the pixel.
14. The method of claim 13 , wherein the setting of the respective gamma to the scaling function for each pixel that is transitional includes setting the respective gamma for the pixel to the scaling function having a formula yx,y=Le S(Ix,y−T) where yx,y is the respective gamma associated with the x, y pixel, L is the specified brightening level, S is a scale factor specifying a sharpness at which the scaling function monotonically increases from the specified brightening level at the specified threshold until the scaling function equals one at the crossover threshold, Ix,y is the input intensity of the x,y pixel, and T is the specified threshold.
15. The method of claim 14 , wherein the crossover threshold is given by a formula U = T - ln L S where U is the crossover threshold with T<U<1.
16. The method of claim 14 , wherein the method further comprises: inputting the specified brightening level, L, that is less than one from an end user; inputting the specified threshold, T, that is greater than zero and less than one from the end user; and inputting the scale factor, S, from the end user.
17. The system of claim 7 , wherein, the output intensity from the gamma transformation monotonically decreases over the range of the input intensity from the specified threshold to the crossover threshold, in which range the scaling function, which provides the respective gamma for each pixel that is transitional, monotonically increases.
18. The system of claim 7 , further comprising: a camera for capturing the input image.
19. The system of claim 7 , wherein the memory device is further configured to store a look-up table for the gamma transformation, and the processor is further configured to read the output intensity for each pixel of the pixels from the look-up table, which output intensity is the input intensity of the pixel raised to a power that is the respective gamma of the pixel.
20. The system of claim 19 , wherein the processor is further configured to set the respective gamma to the scaling function for each pixel that is transitional by setting the respective gamma for the pixel to the scaling function having a formula yx,y=Le S(Ix,y−T) where yx,y is the respective gamma associated with the x,y pixel, L is the specified brightening level, S is a scale factor specifying a sharpness at which the scaling function monotonically increases from the specified brightening level at the specified threshold until the scaling function equals one at the crossover threshold, Ix,y is the input intensity of the x,y pixel, and T is the specified threshold.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
February 20, 2019
November 24, 2020
Browse 5M+ US patents with plain-English claim translations and AI-generated analysis.